Cell recognition and the immune system Flashcards
pathogen definition
organism which cause disease by releasing toxins and destroying/killing tissues and cells
antigen definition
protein usually found on the surface of the membrane of a cell and stimulates an immune response and the production of antibodies
why viruses are seen as non-living (4)
can only reproduce using a living host cell
has attachment proteins
very small (20-300nm)
contains RNA and DNA in a capsid
what are attachment proteins on viruses for
identifies and attaches to host cell
types of non-specific immune responses (2)
physical barriers
phagocytosis
examples and explanations of physical barriers
skin (can get in if broken)
stomach acid (pH 2 kills bacteria in food/ drink)
cilia lining (e.g. in trachea - removes microbes and debris from interior of lungs)
mucus (produced by goblet cells traps pathogens)
definition for phagocytosis
phagocytes ingest and destroy pathogens before they cause any harm
steps for phagocytosis (5)
- Phagocyte is attracted to the chemicals produced by pathogen and attaches to its surface
- Phagocyte engulfs pathogen forming a phagocytic vesicle (phagosome) 3. Lysosomes move and fuse with phagosome
- Lysozymes digest pathogen by hydrolysing cell wall
- Products are absorbed into the cytoplasm of the phagocyte, waste products leave and pathogen antigens are presented on the surface of the phagocyte
types of specific immune response (2)
B cell response
T cell response
what and where are lymphocytes produced
stem cells in the bone marrow
what does the specific immune response respond to (4)
antigens on: cells infected by a virus cells from another individual of the same species toxins secreted by pathogens abnormal self-cells
where do T lymphocytes mature
thymus gland
what response are T cells responsible for
cell-mediated immunity/ cellular response
how are T cells stimulated
when pathogen antigens are presented on the cell membranes of phagocytes (not in body fluids)
Different types of T cells respond to different types of pathogen
steps for T cell response
- Phagocytes engulf pathogen and presents their antigens on their surface
- Receptors on specific helper T cells (TH) bind to antigen on antigen-presenting cells as they have complementary shapes
- This attachment activates the T-helper cells to divide rapidly by mitosis
- Cloned T cells: - Develop into memory T cells allowing a rapid response to same pathogen
- Stimulate phagocytes to engulf the pathogens
- Stimulates B cells to divide and produce antibodies (agglutination)
- Activates cytotoxic T cells (Tc or T-killer cells)
how do cytotoxic T cells work
Kill infected cells by producing a protein called perforin which makes holes in cell membranes so it becomes freely permeable
where do B cells mature
bone marrow
what type of immunity are B cells responsible for
humoral immunity
what is humoral immunity
involves antibodies present in body fluids and blood plasma
Steps for B cell response
- B cell with specific antibody fits onto the antigen on the surface of the foreign cell due to complementary protein shapes
- Antigen enters B cell by endocytosis and is presented on the surface of the B cell
- T-helper cells bind to these antigens
- specific B cell divides by mitosis so all clones produce antibodies specific to the foreign antigen (clonal selection)
- Antibodies attach to antigen on pathogen and destroys it by forming antigen-antibody complexes
- B cells become either plasma cells or memory cells
o Plasma cells secrete antibodies into the blood plasma for the primary immune response
o Memory cells will divide rapidly if the same antigen is present again
what do memory cells do
Produces plasma cells and more memory cells for secondary immune response if the same antigen is present again
clonal selection definition
ability to respond rapidly to specific antigens by cloning complementary antibodies
antibody definition
protein produced by B cells in response to specific antigens on the surface of cells which assists in the destruction of pathogens
how do antibodies assist the destruction of pathogens (2)
- Causes bacterial cells to agglutinate so it is easier for phagocytes to locate and ingest pathogens
- Acts as markers for phagocytes by binding to form antigen-antibody complexes as they are complementary
structure of antibodies
o Have 4 polypeptide chains (2 heavy, 2 light)
o Specific binding sites (variable region) attach to specific antigens
o Constant region for agglutination
o All joined by disulphide bridges
monoclonal antibody definition
single type of antibody produced outside the body by cloning of a single B cell
uses of monoclonal antibodies (2)
monoclonal antibodies therapy
medical diagnosis
what is monoclonal antibodies therapy
monoclonal specific antibodies to antigens are given to patient and attach to receptors of cancer cells blocking the chemical signals that stimulate their uncontrolled growth
benefits of monoclonal antibodies therapy (4)
fewer side effects
not toxic
highly specific
Can attach drugs to antibody
how are monoclonal antibodies used for medical diagnosis
specific monoclonal antibodies interact with antigens/ hormones to produce a antibody-colour complex
ethical issues of monoclonal antibodies (2)
production involves mice
testing on humans may cause major side effects
what does ELISA stand for
enzyme linked immunosorbent assay
what is the ELISA test used for + examples
detects the presence and quantity of a pathogen in a sample
e.g. detect HIV, pathogens such as TB, hepatitis
ELISA test steps (8)
- Pour sample into a well so the antigens in the sample will attach to the surface
- Wash the well to remove unattached antigens
- Add the specific antibody so they bind together forming an antigen-antibody complex
- Wash the well to remove unbinded antibody
- Add a second antibody with enzyme attached to attach to first antibody
- Wash well to remove unattached enzyme
- Add substrate of enzyme to form a coloured product
- Amount of antigen present is relative to the intensity of colour developed
why do the wells in the ELISA test need to be washed after adding stuffs e.g. washing away enzyme
so no enzyme-substrate complexes form with unbound enzymes causing a change in colour
passive immunity definition
introducing antibodies into individuals so no contact with pathogen or antigens
active immunity definition
direct contact with pathogen or its antigen by vaccination or infection stimulates the production of antibodies by the individual’s own immune system
compare active immunity with passive immunity
active immunity takes more time to develop but lasts longer
active has contact with pathogens/antigens
types of active immunity (2)
natural AI
artificial AI
what is natural active immunity
result from individual becoming infected with disease under normal circumstances
what is artificial active immunity
vaccinating the disease into an individual to induce an immune response without suffering symptoms of disease
herd immunity definition
vaccinate the vast majority of the population so it is difficult for a pathogen to spread within a population due to lack of hosts to survive and reproduce
second immune response compared to first (3)
• Greater/ more rapid production of antibodies (skips clonal selection)
o First encounter would take longer to activate B cells
• Memory cells are already present
• Symptoms are not displayed
why might vaccines fail
• fail to induce immunity to those with defective immune systems
o May develop the disease and spread the disease
• Antigenic variability
• many varieties of a particular virus so vaccine not effective against them all e.g. common cold virus
• certain pathogens “hide” from the immune system by concealing themselves inside cells q
• religious, ethical or medical reasons lead to individuals not having the vaccination
antigenic variability defintion
pathogen may mutate frequently so antigen changes suddenly and so the immune system is unable to produce the antibodies to destroy the pathogen
why is antigenic variability a mare + example
immunity is short-lived
e.g. influenza has several antigens so needs several memory cells
ethical issues of vaccines (3)
- production and development involves the use of animals
- may cause side effects (balances with controlling a disease within a population??)
- individuals tested for trial vaccines with unknown health risks
what does HIV stand for
human immunodeficiency virus
what does HIV need to replicate
living host cells
how can HIV be passed on (2)
sexual intercourse
sharing needles
why might there be an increase in HIV diagnoses (3)
more HIV testing
immigration of infected peeps
more heterosexual transmission
what type of virus is HIV and definition
retrovirus
able to make DNA from RNA
o contains reverse transcriptase which catalyses production of DNA from RNA (reverse reaction is catalysed by transcriptase)
Steps for replication of HIV
- virus enters blood stream
- protein on HIV binds to protein on surface of T helper cells
- capsid fuses with the CSM so RNA and enzymes enter the T helper cell
- reverse transcriptase converts the virus RNA into DNA
- DNA moves into the nucleus of T helper cells
- HIV DNA in nucleus makes mRNA (using the enzymes of the cell)which contains the code for making new viral proteins and RNA
- mRNA moves out of nucleus though nuclear pores and uses the cell’s protein synthesis mechanisms to make HIV particles
- synthesised HIV particles break away from T cell with a bit of CSM surrounding which makes their lipid envelope
what does HIV cause
AIDS
what does AIDS stand for
acquired immune deficiency syndrome
how does HIV cause AIDS
HIV reduces the concentration and interferes with normal function of T helper cells
Unable to stimulate enough B cells to produce antibodies or cytotoxic cells
why are antibiotics ineffective on AIDS (2)
no metabolic pathways or cell structures for them to disrupt
no sites for antibodies to work as they have a protein coat rather than murein cell wall of bacterial cells
why might there be less diagnosis of AIDS
early diagnosis
new treatments
how do antibiotics kill bacteria (3)
prevents bacteria from making murein cell walls so they would burst from turgor pressure
- inhibits the enzymes required for synthesis of peptide cross links in cell walls
- weakens cell walls so are unable to withstand the pressure
- bacterial cell bursts and dies
Why specific antibodies detect specific antigens
Antibodies have variable region with specific amino acid sequence
Shape of the binding site is complementary to antigens so can form antigen-antibody complexes
Why are antigens not able to pass through cell surface membranes
Not lipid soluble
Too large to diffuse through
Antigens do not have complementary shapes to bind to carrier proteins
Why would HPV vaccines not be effective on other types of HPV
Other types have different antigens
No memory cells for these types to stimulate secondary immune response so antibodies do not attach to antigen
